The present invention relates to a recycling cooking oven for cooking food at least in part by hot air flow (e.g. hot air impingement), and more particularly to a vented recycling cooking oven providing a substantially or essentially closed but vented cooking environment.
U.S. Pat. No. 5,927,265 discloses a recycling cooking oven for cooking food at least in part by hot air flow and providing a substantially closed environment. The oven comprises a cooking chamber for receiving a stream of hot air from a thermal plenum via a plurality of openings in the cooking chamber, the cooking chamber cooking food therein at least partially with hot air from the plurality of openings and the cooking of such foods adding oxidizable components to the hot air. Means forming a thermal plenum are located upstream of the cooking chamber and include heating means for supplying hot air into the cooking chamber via the plurality of openings. Means are provided for causing the stream of hot air to circulate in a substantially continuous travel path including the thermal plenum, the plurality of openings, and the cooking chamber. A main catalytic converter is disposed in the continuous travel path of the stream of hot air for flamelessly oxidizing oxidizable components in the hot air of the stream leaving the cooking chamber, thereby both to remove them from the hot air of the stream and to release at least some additional heat energy into the hot air of the stream.
Preferably the thermal plenum maintains the reservoir of hot air at a temperature such that the main catalytic converter has an inlet temperature allowing catalytic activity (destruction of oxidizable components) to occur. The oxidizable components may include grease, fats, oils and like hydrocarbons produced by cooking food in the cooking chamber and are preferably oxidizable essentially to carbon dioxide and water.
However, as a practical matter, it is frequently desirable, if not absolutely necessary, to control the exchange of air between the oven cavity interior and ambient in a substantially recycling cooking oven via a vent. The vent enables the planned escape of hot air from the oven. Various factors render such a vent desirable and necessary. First, the natural expansion of the air within the oven as it becomes heated will increase the pressure of the air being circulated. An increase in the pressure of the hot air being circulated may be undesirable since it could result in leakage of the air out of the oven into the ambient atmosphere, or a blast of hot air being directed at a user when the user opens the oven door. Thus, it is preferable to allow the volume of the gas to change (via a vent) so as to maintain a constant gas pressure. Second, during cooking a portion of the moisture evolved from the food product must be vented in order to provide acceptable food surface conditions. Third, if the oven is to have a self-cleaning feature, the various oxidizable components removed from the walls of the cooking chamber must be removable from the oven interior via a vent. Fourth, there exists a certain amount of leakage from ambient air into the oven cavity, which should be compensated for via means of a vent.
For the above and related reasons well recognized by those skilled in the oven art, it is desirable to provide a vent communicating with the ambient atmosphere and the oven interior for diverting an auxiliary vent stream of hot air from the interior of the essentially recycling oven into the vent means.
Use of a vent for communication between the cooking chamber and associated plenums and ducts of the oven and the ambient atmosphere presents new problems if the oven is to comply with various indoor air quality standards and consumer expectations for clean indoor air such as the cleanliness of the auxiliary vent stream emitted into the ambient atmosphere, via the vent means, from the oven interior.
German Patent Application No. 26 40 684, filed Sep. 7, 1976, discloses a recycling cooking oven providing a substantially closed but vented environment. The hot air stream leaving the cooking chamber is bifurcated into a recycling stream which passes through a first or recycling catalytic converter before it is returned to the cooking chamber and a vent stream which passes through a second or vent catalytic converter disposed in the vent. Neither the recycling stream nor the vent stream passes through both catalytic converters; each stream passes only through a respective one catalytic converter. As a result, if the second or vent catalytic converter, is to provide a lower level of oxidizable components than is found in the recycling stream after it passes through the first or recycling catalytic converter, the second or vent catalytic converter must be configured and dimensioned, initially, to reduce the level of oxidizable components in the vent stream to that of the recycling stream after it passes through the first catalytic converter, and, then, it must reduce the level of oxidizable components further to what is deemed an acceptable discharge level. Depending upon the fraction of the total hot air stream being sent through the second or vent catalytic converter, this may require a second or vent catalytic converter of greater dimensions and/or more expensive highly active catalytic material than the first or recycling catalytic converter, thereby placing the oven at an economic disadvantage.
This follows from the fact that in a recycling oven, as disclosed in the aforementioned German application, the first or recycling catalytic converter acts on the entire stream of hot air leaving the cooking chamber (excluding the vent stream). This entire stream will pass through the first or recycling catalytic converter several times. Accordingly, it is only necessary for the first or recycling catalytic converter to remove a fraction (say, 20% by volume) of the oxidizable components on each pass (five passes presumably being sufficient to remove all of the oxidizable components). Therefore the first or recycling catalytic converter may be formed of less expensive and less catalytically active materials and/or be of smaller dimensions than would be the case if it were required that it substantially oxidize all of the oxidizable components present in the recycling stream on each pass. By way of contrast, the second or vent catalytic converter has only one pass in which to remove the oxidizable components in the vent stream to an acceptable discharge level. Accordingly, the second or vent catalytic converter of the above-identified German Application must be made of more efficient catalytically active (hence more expensive) materials and/or of greater dimensions than the first or recycling catalytic converter.
Accordingly, it is an object of the present invention to provide a recycling cooking oven affording a substantially closed but vented environment.
Another object is to provide such an oven including in the vent means an auxiliary catalytic converter, downstream of the main catalytic converter, for further reducing the level of oxidizable components in the vent stream.
A further object is to provide such an oven wherein the vent catalytic converter (due to changes in dimensions and/or catalytic material) is more economical than the main catalytic converter.
Yet another object is to provide such an oven that is self cleaning.
It is also an object of the present invention to provide such an oven which is simple and economical to manufacture, use and maintain.